Method of making welded joints

ABSTRACT

Method of making welded joints between metals of different heat conductivity, and which have a tendency to form intermetallic phases when contacted at high temperatures, such for example as titanium and copper, and titanium and iron. The metal of the better heat conductivity is preheated and the other metal is protected from premature heating by an inert gas stream. Both metals are separated from each other during preheating and that portion ahead of the welding zone.

United States Patent Kiesow et al.

METHOD OF MAKING WELDED JOINTS inventors: Wilhelm Kiesow, Hagen; Gerhard l-leuser, Dortmund, both of Germany Assignee:

Germany Filed: July 16, 1970 App1.No.: 55,395

Foreign Application Priority Data Aug. 21, 1969 Germany ..P 19 42 572.0

US. Cl. ..29/494, 29/198, 29/488,

Int. Cl ..B23k 5/22, B231: 31/02 Field of Search ..29/488, 494, 497, 504, 198

References Cited UNITED STATES PATENTS 9/1948 Cate .;...29/488 10/1948 La Motte..... ..29/494 X l/1950 Von Deventer ..29/497 X 7/1957 Slomin et al. ..29/198 UX 1011958 Beggs ...29/494 X 12/1962 Rossner ..29/494 X INERT Friedrich Uhde GmbH, Dortmund,

3,701,196 [as] on. 31, 1972 l-lorigan, Jr. ..29/ 198 X 3/1964 3,213,532 10/1965 Glaseretal ..29/494x 3,359,142 12/1967 Ward,Jr ..29/497x OTHER PUBLlCATlONS Primary Examiner-John F. Campbell Assistant Examiner-Ronald J. Shore Attorney-Malcolm W. Fraser ABSTRACT Method of making welded joints between metals of different heat conductivity, and which have a tendency to form interrnetallic phases when contacted at high temperatures, such for example as titanium and copper, and titanium and iron. The metal of the better heat conductivity is preheated and the other metal is protected from premature heating by an inert gas stream. Both metals are separated from each other during preheating and that portion ahead of the welding zone.

5 Claims, 1 Drawing Figure GAS PATENTEDncm I972 INERT GAS INVENTORS WILHELM KIESOW GERHARD HEUSER ATTORNEY 1 METHOD or MAKING WELDED JOINTS BACKGROUND OF THE INVENTION The present invention relates to a method for the fabrication of welded joints, under inert gas shielding, between metals of different heat conductivity and having a tendency to form intermetallic phases when coming in contact at an elevated temperature, such as titanium/copper, titanium/iron.

Whenever any constructional member is exposed to different simultaneous stresses, for example by tension, compression, heat, corrosion, cavitation and/or the passage of electrical current, the use of high grade metallic materials of construction is imperative. In case of localized stresses-within the same constructional member, economic considerations frequently call for composing the constructional member of different materials in line with the different kinds of stresses. Referring to electrolysis plants it is desirable, for example, to use titanium for the anode and copper for the current conductor to the anode. The bond between copper and titanium should be perfect enough to hold voltage losses at this point at a minimum or even at zero.

It is known that the bond must be as intimate as possible to meet said requirement. Known designs incorporate bolted, riveted, or clamped joints which are, however, highly problematic because-of their tendency to be attacked by contact corrosion or corrosion cracking under the influence of electrolysis-products owing to inevitable leakages. The voltage drop at these points also causes a considerable temperature rise in the metal, which is undesirable. In addition, the anode current efficiency becomes subject to fluctuations owing to the difference in voltage distribution at the numerous anodes. A welded joint between titanium and copper might offer ideal current carrying characteristics. However, it has so far been impossible to achieve a permanent bond by welding the two metals together.

For the fabrication of welded joints between metals of different heat conductivity, such as combinations of titanium/copper and titanium/iron, the material with the better heat conductivity, that is the higher heat dissipation, must be preheated so that the two metals within the-welding zone may be at essentially the same temperature during the welding procedure. Preheating can be performed along known methods. For the welding of copper or iron with titanium the preheat temperature is within a range where these two metals,

- when contacted with titanium, pass into solution with the titanium to form intermetallic phases that lead to the embrittlement of the welding zone. Consequently, it is generally considered impracticable to weld together two metals, such as titanium/copper or titanium/iron, that have a tendence to forming intermetallic phases.

SUMMARY OF THE INVENTION In order to arrive at the most favorable combination of materials and the best possible material bond, the object of the invention is to find a welding procedure that provides a joint whose resistance is approximately equal to or better than that of the materials to be joined by welding.

According to the invention, the problem is solved in that the metals to be joined by welding are kept apart both during preheating and during the welding procedure ahead of the welding zone. Depending on the precision of previous machining of the surfaces to be joined by welding, the gap should be 0.2 to 3 mm. In addition, the metal of better heat conductivity shall be preheated with the aid of known heating facilites. The titanium shall preferably be protected from premature heating by means of an inert gas stream. Depending on the configuration of the two elements to be joined, the

gap might be maintained by the inert gas pressure.

The invention incorporates the particular advantage that the welded joint exhibits a mechanical resistance which is superior to that of copper. Referring to current carrying characteristics the joint is free of transition resistance with its undesirable consequences.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing, a copper sleeve 1 is to be I welded to a titanium anode 2 in the form of a flat plate. For this purpose, an inert gas feed tube- 3 is inserted into the sleeve 1 so that the inert gas may leave the tube at 4 and escape into the atmosphere through a gap 5 between the sleeve 1 and the titanium anode 2. The inert gas blanket prevents any access of air to the welding zone 8.

The workpieces 1 and 2 are fixed in place with the aid of conventional means to prevent physical contact. Depending on the configuration of the elements to be welded together, 'the gap between the two elements, which should be between 0.2 and 3 mm, can also be maintained .by the exit pressure of the inert gas as shown on the drawing.

By means of aheating system 7, such for example as an electrically energized ring, the temperature of the sleeve is raised to approximately 800 C. As soon as the sleeve 1 has reached this temperature, the heating system 7 is removed or shut down, and welding is started at point 8. Welding may be accomplished by employing a consumable electrode of titanium wire melted with the aid of an inert gas welding torch. More precisely, the sleeve 1 is first tack welded to the plate 2 on this side before starting the circumferential weld on the opposite side. This method ensures a strong and corrosion resistant joint with optimum current carrying characteristics.

What we claim is:

l. A method of making a welded joint between pieces of copper and titanium, said method consisting of the steps of arranging the pieces in juxtaposed relation with a small gap separating the pieces, guiding an inert gas stream through said gap, preheating the piece of copper, the piece of titanium being shielded by the inert gas stream from premature heating, and then performing the welding operation progressively while the pieces to be welded together are held separate from each other ahead of the welding zone.

2. A method as claimed in claim 1, in which the spacing between the work pieces is 0.2 to 3 mm.

3. A method as claimed in claim 1, in which the gap between the work pieces is maintained by the pressure of the inert gas.

4. A method as claimed in claim 1, in which onework piece is flat and is of titanium and the other is sleeve-like and is of copper, and in which the inert gas is delivered through the sleeve-like piece to the gap or 

1. A method of making a welded joint between pieces of copper and titanium, said method consisting of the steps of arranging the pieces in juxtaposed relation with a small gap separating the pieces, guiding an inert gas stream through said gap, preheating the piece of copper, the piece of titanium being shielded by the inert gas stream from premature heating, and then performing the welding operation progressively while the pieces to be welded together are held separate from each other ahead of the welding zone.
 2. A method as claimed in claim 1, in which the spacing between the work pieces is 0.2 to 3 mm.
 3. A method as claimed in claim 1, in which the gap between the work pieces is maintained by the pressure of the inert gas.
 4. A method as claimed in claim 1, in which one work piece is flat and is of titanium and the other is sleeve-like and is of copper, and in which the inert gas is delivered through the sleeve-like piece to the gap or space between the work pieces.
 5. A method as claimed in claim 4, in which preheating of the sleeve-like piece is performed by applying heat to the outside thereof. 